Polymer-based composite catholyte structures have been investigated in a continuing effort to increase the charge/ discharge capacities of solid-state lithium thin-film electrochemical cells. A cell according to this concept contains the following layers (see figure):

  • An anode current-collecting layer, typically made of Cu;
  • An Li metal anode layer;
  • A solid electrolyte layer of Li3.3PO3.8N0.22 ("LiPON") about 1 to 2 μm thick;
  • The aforementioned composite catholyte layer, typically about 100 μm thick, consisting of electronically conductive nanoparticles in an Li-ion- conductive polymer matrix; and
  • A metallic cathode current collector, typically made of Mo and about 0.5 μm thick.

A Polymer-Based Composite Catholyte Layer may be the key to high charge/discharge capacity in an Li thin-film cell. In prototype cells, the catholyte layers consisted of LiCoO2, polyethylene oxide, lithium trifluoromethanesulfonate, and carbon black.
In the fabrication of such a cell, the anode current collector (or, alternatively, the Li anode layer if already present as explained in the next paragraph) is first used as a substrate, onto which the Li3.3PO3.8N0.22 layer is deposited. The composite catholyte layer is then cast onto the Li3.3PO3.8N0.22 layer. Next, the cathode current collector is deposited on, or pressed into contact with, the composite catholyte layer.

If the anode current collector is a Cu film on a flexible substrate (as in prototype cells) or if it is something similar, the Li anode layer can be formed by plating of Li on the anode current collector during the first charge. Alternatively, the anode layer can be made, at the outset, of a thin film of Li; if this were done, the cell could retain a greater fraction of its capacity over many cycles because the film could be made to contain a slight excess of Li that would be available to replace some Li that is lost to the surroundings during cycling.

Inasmuch as Li3.3PO3.8N0.22 is an amorphous, flexible material, the cell as a whole can be a free-standing, flexible structure. Theoretically, the capacity of the cell can equal or perhaps exceed that of a typical state-of-the-art lithium thin-film cell. The inclusion of the Li3.3PO3.8N0.22 is expected to result in extended lifetime and enables the use of Li in metallic form because the hazards associated with the combination of metallic Li and liquid electrolyte are not present. Further, it is anticipated that the cell would have long (relative to prior Li thin-film cells) cycle life at temperature up to 150 °C, provided that the proper cathode material is selected.

The capacities of the prototype cells thus far have been below theoretically attainable values. It seems likely that the theoretical values could be approached by selecting the proper cathode material and including thin Li anode films at the outset.

This work was done by Jay Whitacre, William West, Keith Chin, and Sekharipuram Narayanan of Caltech for NASA's Jet Propulsion Laboratory.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:

Innovative Technology Assets Management

JPL

Mail Stop 202-233

4800 Oak Grove Drive

Pasadena, CA 91109-8099

(818) 354-2240

E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Refer to NPO-41068, volume and number of this NASA Tech Briefs issue, and the page number.

Topics:
Casting Composite materials Electrolytes Fabrication Lithium Manufacturing processes Materials Metal finishing Metallurgy Metals Plating Polymers
This Brief includes a Technical Support Package (TSP).
Document cover
Polymer-Based Composite Catholytes for Li Thin-Film Cells

(reference NPO-41068) is currently available for download from the TSP library.

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This article first appeared in the July, 2008 issue of NASA Tech Briefs Magazine (Vol. 32 No. 7).

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Overview

The document presents a technical support package from NASA's Jet Propulsion Laboratory (JPL) detailing advancements in lithium battery technology, specifically focusing on polymer-based composite catholytes for lithium thin-film cells. The research addresses the limitations of traditional thin-film batteries, which typically consist of a metallic current collector, a thin film cathode, a lithium phosphorus oxynitride (LiPON) electrolyte, and a thin film anode. These batteries, while exhibiting excellent performance, are constrained by their capacity, which does not exceed approximately 200 μAh/cm² due to the thickness limitations of the cathode film and the low ionic conductivity of pure ceramic materials.

To overcome these challenges, the document discusses the development of solid composite cathodes, or cathalytes, which combine a powder cathode material with an electronically conductive powder in a polymer-based ionically conducting matrix. This innovative approach allows for the creation of thicker cathode layers that can enhance ionic and electronic conductivity, thereby increasing the overall capacity of the battery. The proposed battery cell fabrication method integrates a thin film inorganic electrolyte layer, a lithium metal anode, and a high-capacity cathalyte, resulting in a more efficient energy storage solution.

The document highlights the potential for optimizing cathode materials and incorporating a lithium thin film on the anode side to significantly boost cell capacity, which has been observed to be much lower than theoretically possible in prototype cells. The results indicate that cells fabricated using this method are functional as secondary batteries, showcasing a strong foundation for further development and reporting in new technology reports.

Additionally, the document emphasizes the promising results from the thin-film solid-state battery community, noting that these batteries exhibit excellent cycle life—approaching 100,000 cycles—and high voltage stability in the presence of metallic lithium. The fabrication techniques employed, such as sputtering and thermal evaporation, contribute to the overall performance and reliability of the batteries.

In summary, this technical support package outlines a novel approach to lithium battery fabrication that marries thin-film technology with polymer-based composite cathodes, paving the way for advancements in energy storage solutions with applications in aerospace and other fields.